A known a crushing apparatus for crushing concrete pillars or beams by opening and closing a pair of arms having crushing blades attached to the ends thereof. In crushing concrete structures using such type of crushing equipment, the ends of the arms must be widely opened when the concrete pillars or beams to be destroyed have a large diameter. Furthermore, in order to crush pillars or beams of such large diameter, a large crushing force is required because of such large diameter. However, once the pillars or beams are cracked first crushed, they can be crushed thereafter completely without requiring a force as large as the initial force.
On the other hand, the pillars or beams having a relatively small diameter for which the ends of the arms are not required to be widely opened do not require a large crushing force.
As a drive source for opening and closing the arms, that is, as a drive source for conferring a crushing force onto the crushing blades attached to the arms, normally a hydraulic cylinder is used. When using a hydraulic cylinder, it is necessary for the piston to have a large pressure-receiving area in order to produce a larger crushing force. However, the increase in the pressure-receiving area of the piston entails a reduction in the moving speed of the piston rod, that is, the reduction in opening and closing speed of the arms, which reduces the crushing operation efficiency. The concrete structures comprise pillars and beams range from large to small-diameter. There is no need for a large crushing force to be applied to pillars or beams of larger diameter once they have been crushed and cracked. Nevertheless, in order to crush pillars or beams of large-diameter, a hydraulic cylinder fitted with a piston having a large pressure-receiving area must used as a drive source for opening and closing the arms of the hydraulic cylinder. Thus, the same hydraulic cylinder must be used for crushing pillars or beams of small-diameter or the once crushed cracked pillars or beams, thereby reducing the efficiency of the crushing operation.
In order to solve the above problems, applicant invented an apparatus for crushing concrete structures using a telescopic hydraulic cylinder as a drive source for opening and closing the arms of the crushing apparatus, and has filed a patent application in Japan. The content of this invention is disclosed in Japanese Patent Laid-open Publication No. 63-40061.
The telescopic cylinder comprises a plurality of hydraulic cylinders, each cylinder including an oil port for the backward stroke provided in the outer periphery of the cylinder and communicating with the end of the piston-rod-side oil chamber, and an oil port for the forward stroke provided in the cylinder bottom, whereby, the cylinders of respective stages are reciprocated by supplying the hydraulic oil through the oil ports.
FIG. 4 illustrates a conventional telescopic hydraulic cylinder by way of example. This telescopic hydraulic cylinder comprises an outer cylinder 102 and a plurality of inner cylinders 101, each being fitted into another in sequence and having the above-described constitution. The cylinders are caused to be displaced forward by virtue of the hydraulic oil introduced through an oil port 103 provided in the cylinder bottom of the outer cylinder 102 in descending order according to the size of the cross-sectional area of cylinder bottom, thereby ensuring an initial high output and forwardly displacing the cylinders having a smaller sectional area in sequence in accordance with the extension of the stroke to speed up the protruding action in inverse proportion to the decrease in the output. Such output characteristics of the conventional cylinder are suitable for such hydraulic equipment as requiring a high output at initial drive and having a load decreasing in accordance with the increase in the extension of the stroke, for example, for a drive source for a load-carrying platform of a dump truck, or for a drive source for a crushing equipment for concrete structures or others. However, in the case of the crushing equipment for concrete structures or others on which a retractive force arising from the weight of the object to be driven will not act, there is a need for means for retracting the once extended hydraulic cylinder to its initial state. For the retracting action in the example shown in FIG. 4, the hydraulic oil introduced through an oil port 104 provided at the end of piston-rod-side oil chamber of the outer cylinder 102 is supplied into the piston-rod-side oil chambers of the respective cylinders by way of oil ports 105 provided in outer peripheries of the cylinder in the vicinity of the cylinder bottoms of the cylinders 101, oil passages 106 extending through the interior of the cylinders 101, and then oil ports 107 provided at the end of the piston-rod-side oil chamber. The retractable forces to be applied on the respective cylinders 101 depend on, for example, the relationship between the diameters of the cylinders and the diameters of the cylinder bottoms. More specifically, the retractive action of a cylinder of smaller diameter will not necessarily precede that of a cylinder having a larger diameter. In case a cylinder of larger diameter precedes a cylinder of smaller diameter in the retractive action, the subsequent protracting action will always starts from the cylinder of larger diameter, thereby disabling the high-speed retractable action at the top of the extended stroke.
Accordingly, in order to realize the superior characteristics of the telescopic hydraulic cylinder such that not only initial high output is ensured but also a high-speed retractive action is possible in the extended state of stroke, it is always necessary that the retractable action be started from a cylinder of smaller diameter.
Thus, in view of this point, as disclosed in the Japanese Patent laid-open Publication No. 63-40061, the present applicant has developed a telescopic hydraulic cylinder in which there are provided oil ports separately communicating with the piston-rod-side oil chambers of the smaller-diameter cylinders, and with the piston-rod-side oil chamber of the larger-diameter cylinder receiving the smaller-diameter cylinders under the condition where the piston rods of the smaller-diameter cylinders are fully extended forward, and the hydraulic oil is supplied in sequence from the piston-rod-side oil chamber of a smaller-diameter cylinder to cause the retractive action to take place in sequence from a smaller-diameter cylinder. Simultaneously, the present applicant has also proposed a crushing equipment for concrete structures using such telescopic hydraulic cylinder as a drive source for opening and closing of the arms. The telescopic hydraulic cylinder disclosed in the Japanese Patent Laid-open Publication No. 63-40061, however, has a shortcoming such that the supply of the hydraulic oil into the piston-rod-side oil chambers of the respective cylinders must be controlled separately for the retractive actions, thereby complicating the opening and closing operation of arms.